Several phase control and/or regulating systems are known. In many cases these are merely control systems in which a particular speed is set in a trigger circuit by setting of a time constant.
Rotary speed control systems may use a tacho-generator coupled to the motor from which an electrical signal for the actual speed value is derived. Such a control system has the disadvantage of being relatively slow because as a rule the mechanical time constant of the motor is part of the control process or the stabilizing process. The control circuits of full wave control systems for universal motors without tacho-generators are still relatively expensive because either the entire control circuit must be a DC circuit or at least the feedback signal must be rectified and/or the feedback signal is fed to active semiconductor elements for amplification and for the processing.